Preparation of graft copolymer and paint use thereof

ABSTRACT

Preparation of a graft copolymer prepared by reacting a cellulose ester and a mono- or a di-ester of maleic or fumaric acid, thereby obtaining a cellulose derivative bearing a polymerizable double bonding, and then copolymerizing said cellulose derivative with other copolymerizable monomer(s). The invention also includes a coating composition based on the thus obtained graft copolymer.

FIELD OF INVENTION

The present invention relates to a method for preparing graft copolymersof cellulose derivatives with other copolymerizable monomers. Theinvention also concerns a coating composition based on the graftcopolymer thus obtained.

BACKGROUND OF THE INVENTION

Recently, attention has been concentrated, in the paint industry to aresinous copolymer of cellulose acetate butyrate (hereinafter referredto CAB) and vinyl monomer, having excellent drying properties, hardnessand other desired properties.

To obtain such resinous copolymer, various methods have been proposedincluding:

(1) A method wherein CAB is directly copolymerized with vinylmonomer(s), using an organic peroxide as a polymerization initiator, asshown, for example, in Japanese Patent Application Kokai Nos. 115126/74,ibid 133472/80, ibid 54301/80, Japanese Patent Publication Nos.37683/75, ibid 5659/76, ibid 5660/76 and ibid 2978/83.

(2) A method wherein specified amounts of acid, acid anhydride, acidchloride or isocyanate are first reacted with the hydroxyl groups ofCAB, thereby introducing to the CAB molecule mercapto groups, a groupfrom which hydrogen may be easily drawn or unsaturation bonding, andthen vinyl monomer(s) is (are) graft-polymerized, as given, for example,in Japanese Patent Application Kokai Nos. 80192/73; ibid 48030/75; ibid48031/75; Japanese Patent Publication No. 8105/80.

(3) A method wherein graft polymerization is carried out using a Co⁶⁶ orCe⁺⁺⁺ salt.

However, in any of the known methods, there is a serious drawback inthat the grafting rate is extremely low. Therefore, when the resinoussolution thus obtained is applied and dried, there always results acoating with white blooming.

Moreover, the resinous product has poor compatibility with other resinsas, for example, acrylic resins, polyester resins, high styrenecontaining acrylic resins and the like, and the product has only limitedsolubility in various solvents, such as toluene, xylene and otherpaint-use solvents.

The above is especially true when CAB is reacted with maleic anhydrideor maleic acid, in that no CAB graft copolymer suitable for paint usehas been obtained. The inventors, having paid attention to the fact thatCAB has a number of ester bondings, such as an acetate and a butyrate,besides hydroxyl groups, have endeavored to utilize these functionalgroups for the introduction of polymerizable unsaturation bonding andhave succeeded in finding an ingenious way of reacting cellulose esterand mono- or diester of maleic or fumaric acid for that purpose.

On the present basis of this finding, the invention has been made.

SUMMARY OF THE INVENTION

According to the present invention, there is provided a method forpreparing a graft copolymer comprising copolymerizing a cellulosederivative bearing copolymerizable double bonding and copolymerizablemonomer(s), characterized in that the cellulose derivative is obtainedby the reaction of the cellulose ester and mono- or di-ester of maleicor fumaric acid.

The invention also provides a coating composition based on the graftcopolymer thus prepared.

PREFERRED EMBODIMENTS OF THE INVENTION

Since maleic or fumaric esters are wanting in self-polymerizationtendencies, they can be safely used in reactions at higher temperaturesfor a longer duration of time, without the fear of gel formation.

When a cellulose ester is reacted, directly or in an inert organicsolvent, with a mono- or a di-ester of maleic or fumaric acid underheating and optionally in the presence of a catalyst as dibutyl tinoxide, various reactions, consisting mainly of ester-exchange reactionsbetween the ester moiety of said cellulose ester that of maleic orfumaric acid and accompanied by reactions between the hydroxyl group ofthe cellulose ester and the ester moiety of said acid and between thehydroxyl group of the cellulose ester and carboxyl of the half ester ofsaid acid, may be carried out and thus the copolymerizable doublebonding can be easily and effectively introduced in the cellulosemolecule.

The progress of such reactions may be easily detected by the UVabsorbance through liquid chromatography using a UV absorptionphotometer or Gel-permeation chromatography (GPC) and tracing the doublebonding introduced.

When the progress of the reaction was actually examined with theaforesaid method in both cases of direct reaction between the celluloseester the maleic acid or maleic anhydride and of the reaction betweencellulose ester and di- or mono-ester of maleic or fumaric acid (atequimolar quantities, and at the same temperature and same reactiontime), it was found that the former showed a belated increase in UVabsorbance, indicating an extremely slow progress of reaction, than thelatter.

The same was also supported by the following fact.

That is, when the respective resinous varnish was applied, the formervarnish gave a white turbid coating, whereas the latter a clear uniformcoating.

This may be interpreted as follows. In the latter case, there was ahigher reaction rate and hence a higher grafting rate, which might bethe reason for the resulting clear uniform coating.

Even in the case of reaction with maleic acid or maleic anhydride, onemay contemplate using a larger quantity of such acid to get the sameextent of high reation rate as obtained with the mono- or di-ester offumaric acid or the like. However, in that case, since a considerablequantity of unreacted maleic acid or maleic anhydride remains in thesystem and the resulted cellulose product would possess an end carboxylgroup, there results a resinous product with a very high acid value,which might cause the turbidity and clouding of the varnish. This isalso undesired from the standpoint of weather resistance of the coatingbecause it causes yellowing, white blooming, cracking or the like.

Thus, in the present invention, a cellulose ester is first reacted witha mono- or a di-ester of maleic or fumaric acid, which is one of thecharacteristic features of the invention. As the starting material, anyof the cellulose esters may be satisfactorily used, as for example,cellulose acetate, cellulose acetate propionate, cellulose acetatebutyrate and the like. However, from the standpoint of solubility,viscosity and the like, preference is given to cellulose acetatebutyrate and especially to members having an acetylation degree of 1 to34% by weight, a butyrylation degree of 16 to 60% by weight and avisocosity measured by ASTM-D-134315 of 0.005 to 20 seconds. Morespecifically, the following commercialized products may be specifically,advantageouly used: CAB-551-0.01, CAB-551-0.2, CAB-531-1, CAB-500-1,CAB-381-0.1, CAB-381-0.5, CAB-381-20 and the like (Trade Marks ofcellulose acetate butyrates manufactured by Eastman Chemical Products).

As the mono- or di-ester of maleic or fumaric acid, one may usemono-methyl maleate, mono-ethyl maleate, mono-butyl maleate, 2-ethylhexyl maleate, dimethyl maleate, diethyl maleate, dibutyl maleate,di-2-ethyl hexyl maleate, dimethyl fumarate, di-ethyl fumarate, dibutylfumarate, di-2-ethyl hexyl fumarate and the like. These are, however,only examples and one may use any of the mono- or di-esters of theseacids.

Next, in the present invention, thus obtained cellulose derivativehaving a copolymerizable double bonding is reacted with otherpolymerizable monomer(s) to give the desired graft copolymer.

As the polymerizable monomer, any of the vinyl series monomers havingα,β-ethylenically unsaturation bonding may be used. Examples of themonomers include the following:

(1) vinyl monomers such as styrene, vinyl toluene, α-methyl styrene,vinyl acetate, acrylonitrile, methacrylonitrile and the like,

(2) alkyl or cycloalkyl esters of acrylic or methacrylic acid such asmethyl acrylate, methyl methacrylate, ethyl acrylate, ethylmethacrylate, n-butyl acrylate, n-butyl methacrylate, iso-butylacrylate, iso-butyl methacrylate, t-butyl acrylate, t-butylmethacrylate, cylcohexyl acrylate, cyclohexyl methacrylate, 2-ethylhexyl acrylate, 2-ethyl hexyl methacrylate, lauryl acrylate, laurylmethacrylate, stearyl acrylate, stearyl methacrylate, and the like,

(3) hydroxyalkyl esters of acrylic or methacrylic acid such as2-hydroxyethyl acrylate, 2-hydroxyehtyl methacrylate, hydroxypropylacrylate, hydroxypropyl methacrylate and the like,

(4) α,β-ethylenically unsaturated carboxylic acids such as acrylic acid,methacrylic acid, itaconic acid, crotonic acid and the like,

(5) acrylamides or methacrylamides such as acrylamide, methacrylamide,N-methylacrylamide, N-ethyl methacrylamide, N-methylol acrylamide,N-methylol methacrylamide, N,N-dimethyl acrylamide, N,N-dimethylmethacrylamide, N-n-butoxymethyl acrylamide and the like,

(6) glycidyl group bearing vinyl monomers such as glycidyl acrylate,glycidyl methacrylate, allyl glycidyl ether and the like.

These monomers may be used each singularly or in the combination of 2and more in various ratio depending on the film properties and coatingapplications desired.

The weight ratio of said CAB derivative to said monomer(s) may also bevaried in a considerable range and however, it is usually within therange of 1 to 95 weight % of the former: 99 to 5 weight % of the latter.

The copolymerization is usually carried out in a solvent and in thepresence of a radical initiator.

Examples of such solvents, which may be used each singularly or in anycombination, are benzene; alkyl benzenes like toluene and xylene;alcohols like n-butanol, isobutanol and the like; acetic acid esters;ketones and the like.

Examples of radical initiators are peroxides such as benzoyl peroxide,lauroyl peroxide, dicumyl peroxice and the like; hydroperoxideinitiators such as t-butyl hydroperoxide, cumene hydroperoxide and thelike; ketone peroxides and per-ester initiators; azo series initiatorssuch as azobis isobutyronitrile and the like.

In this reaction, one may use a conventional chain transfer agent, too.The copolymerization may be carried out according to normal procedureswhich per se are well known in the art. Thus, in the present method, acopolymerizable unsaturation bonding originating in the mono- or thedi-ester of maleic or fumaric acid can be introduced in a higherreaction rate into CAB, to which the vinyl monomer is effectivelygrafted through radical polymerization.

Therefore, the reaction product is characterized by having a highergrafting rate, which makes for good compatibility with high styrenecontaining acrylic resin and other paint use resins, and which isexcellent in solubility in solvents.

Further more, even if it is applied alone as a clear coatingcomposition, an excellent clear film can be obtained. In that sense, thepresent resin should be clearly distinguished from the conventional CABgraft copolymer. In the second aspect of the invention, there isprovided a coating composition to be used as a base coat in a two-coatone-bake coating system comprising an acrylic graft copolymer obtainedby reacting a cellulose ester with a mono- or a di-ester of maleic orfumaric acid, thereby introducing a copolymerizable double bonding intothe cellulose molecule, and thereafter copolymerizing the same withother polymerizable monomer(s), and a crosslinking agent.

In a 2-coat 1-bake coating system, film coatings are prepared byapplying a base coat, applying, without baking, a clear coat and thensubjecting to a baking operation. In that base coating composition,metallic powders, such as aluminum are usually contained and therefore,in order to have a good control of the arrangement of said powders inthe base coat, a device has to be made to bring the viscosity of theapplied and uncured base coating to a higher level, thereby preventingthe possible movement of said powders in the coating.

At the same time, the clear coating should preferably be based on aresin which is incompatible with that of base coat and/or solvent towhich the base coat can hardly be dissolved. Recently, there is interestin a base coat blended with a cellulose derivative because of the rapidincrease in viscosity of its applied coating and it is not dissolved bythe top coat composition. However, heretofore the proposed cellulosederivatives have been, in general, quite poor in compatibility withacrylic or amino resins to be blended therewith and hence have adrawback in that the blended composition or coating becomes turbid orseparates during storage.

As an alternative, the technique of using a graft copolymer of a acrylicresin and cellulose derivative as a resinous vehicle has also beenproposed.

However, the proposed graft copolymers previously used, though givingsomewhat improved results as compared with those of the mere mechanicalblends with cellulose derivatives, do not fully solve the aforesaidproblems and further improvements are still needed for these types ofresins.

The inventors have now surprisingly found that the present graftcopolymer is quite useful as a resinous vehicle for the base coat,giving a quick increase in viscosity after application, resulting in noturbidity or white blooming of the base coat, and which are compatiblewith acrylic or amino resins and excellent in storage stability.

Besides that, the present coating is quite excellent in appearance andespecially in the desired properties of the metallic coating as, forexample, its metallic feeling, metallic whiteness, metallic mark, glossand the like, when compared with those of heretofore proposedCAB-acrylic resin blends or grafted polymers. The present base coat canwell withstand the attack of the top coating.

These characteristics are believed, up to the present day, to be due tothe improved grafting rate coming from the particular steps used in thepresent invention.

In the present coating composition, the graft copolymer prepared by thepresent process is combined with a crosslinking agent.

Examples of such crosslinking agents are amino resins, polyisocyanatesand other similar members customarly used in the related area.Particularly, preferred members are alkoxylated melamine formaldehydecondensation products as methoxylated methylol melamine, isobutoxylatedmethylol melamine, n-butoxylated methlol melamine and the like. Thecompounding ratio of said acrylic graft copolymer and amino resin is ingeneral in a range of 60/40 to 90/10.

In the present coating composition for base coat use, one may use,besides said acrylic graft copolymer and amino resin, various solvents,metallic powders such as aluminum powder, coloring matter such aspigments and dyestuffs, fillers, surface conditioner (e.g. the siliconseries, the acrylic resinous series) and the like.

As the coloring matter, any of the known pigments and dyestuffs forcoating use may be satisfactorily used, including metal oxides, metalhydroxides, metallic powders, metal sulfides, metal sulfates, metalcarbonates, lead chromate and other salts, carbon black, organicpigments, organic dyestuffs and the like. The present coatingcomposition may also include fillers such as silica, talc and the likeand other resins than said acrylic graft copolymer and amino resin, likeacrylic resins and polyester resins. The coating composition may beapplied on a substrate according to a normal precedure and without beingbaked, and a clear coat may successfully be applied thereupon.

As the clear coat, preference is given to a thermo-setting acrylic resintype composition, however, any of the known clear top-coat compositionsmay be satisfactorily used providing it has good interlaminar strengthto the base coating and improved weather resistance.

Among them, the most preferable members are believed to be the clearcoatings based on the combination of acrylic resin containing hydroxybearing monomers and amino resins such as n-butoxylated methylolmelamine, isobutoxylated methylol melamine, and methoxylated methylolmelamine. However, the invention is not to be limitted to theexemplified members and other thermosetting clear coatings such as, forexample, a aminoalkyd resin base coating, may be satisfactorily useddepending on the film properties required.

After application of said base coat and clear coat, the coatings aresubjected to a baking operation in a usual way, whereby baked films areobtained with excellent appearance. The present technique is especiallyuseful in the automobile industry.

The invention shall be now more fully explained in the followingExamples. Unless otherwise stated, all parts and percentages are byweight.

EXAMPLE 1

Into a reaction vessel fitted with stirrer, thermometer, refluxcondenser and nitrogen gas inlet, were placed 400 parts of CAB-551-0.2(trade mark of Cellulose acetate butyrate, manufactured by EastmanChemical Products), and 500 parts of xylene and the mixture wasgradually heated. After confirming the complete dissolution of CAB, 80parts of mono-butyl maleate, 0.8 part of dibutyltinoxide and 20 parts ofxylene were added and the mixture was reacted, while stirring thereaction mixture and introducing nitrogen gas, at 145°-150° C. for 7hours. After completion of the reaction, 720 parts of toluene, 200 partsof xylene and 720 parts of butyl acetate were added to obtain a resinoussolution of Cellulose acetate butyrate having a double bondingcopolymerizable with other monomer(s).

When subjected to Gel-permeation chromatography (hereinafter called asGPC), the double bonding bearing cellulose acetate butyrate resin showedh₁ /h₂ =2.05, whereas the starting clellulose acetate butyrate showed h₁/h₂ =0.14. Wherein, h₁ represents the height of peak measured by 254 nmUV absorption photometer for the eluent showing maximum peak bydifferential refractometer and h₂ represents the height of peak measuredby a differential refractometer. The increase in UV absorbance thusdetected was a clear indication of the introduction of double bondinginto the cellulose acetate butyrate molecule. In the following Examples,the increase in UV absorbance due to the introduction of double bondingto cellulose acetate butyrate was measured in the same way. The resinoussolution thus obtained was a clear solution having a non-volatilecontent of 17.0%, a viscosity of A-B and a color number of 1.

137.5 parts of said resinous solution and 7.5 parts of butyl acetatewere placed in a reaction vessel fitted with a thermometer, a stirrer,reflux condenser, a nitrogen gas inlet and a dropping funnel, and themixture was heated to 120° C. and stirred, while introducing nitrogengas. At that stage, the following mixture of vinyl monomers andpolymerization initiator was gradually added, while keeping thetemperature, from the dropping funnel in 3 hours.

    ______________________________________                                        styrene             40         parts                                          2-hydroxyethyl methacrylate                                                                       16.2                                                      methacrylic acid    1.1                                                       methyl methacrylate 19.6                                                      n-butyl acrylate    12.0                                                      i-butyl methacrylate                                                                              11.1                                                      t-butyl peroxy 2-ethylhexanoate                                                                   4                                                         total               104        parts                                          ______________________________________                                    

After 30 minutes from the completion of said addition, a mixed solutionof 0.5 part of t-butyl peroxy-2-ethylhexanoate and 5 parts of butylacetate was dropped in over 30 minutes and thereafter, the mixture wasmaintained at 120° C. for 1.5 hour. The thus-obtained graft copolymersolution was a clear solution having a non-volatile content of 50.2%, aviscosity of Z₂ and a color number of less than 1. When the resinoussolution was applied on a glass plate and the solvent was removed, auniform clear coating was obtained.

EXAMPLE 2

400 parts of cellulose acetate butyrate (CAB-551-0.2) and 500 parts ofxylene were placed in a similar reaction vessel as stated in Example 1and the mixture was gradually heated to melt the cellulose acetatebutyrate. After comfirming the complete solution of CAB, 80 parts ofdibutyl fumarate, 0.8 part of dibutyl tinoxide and 20 parts of xylenewere added and the mixture was heated and stirred, while introducing anitrogen gas stream, at 145° to 150° C. for about 7 hours. Aftercompletion of the reaction, 720 parts of toluene, 200 parts of xyleneand 720 parts of butyl acetate were added to obtain a resinous solutionof cellulose acetate butyrate having a double bonding copolymerizablewith other monomer(s). By the GPC analysis, it was found that h₁ /h₂ was1.95, whereas the same ratio of the starting CAB was 0.13. Thethus-obtained clear resinous solution had a non-volatile content of17.5%, viscosity of C-D and a color number of 1.

137.5 parts of thus obtained resinous solution and 7.5 parts of butylacetate were placed in a similar reaction vessel as used in Example 1,and the mixture was heated to 120° C. and stirred, while introducingnitrogen gas. While maintaining the same temperature, a mixture of vinylmonomers and a polymerization initiator hereinunder stated was addeddropwise in at a constant speed from a dropping funnel in a period of 3hours.

    ______________________________________                                        styrene             40         parts                                          2-hydroxyethyl methacrylate                                                                       16.2                                                      methacrylic acid    1.0                                                       methyl methacrylate 2.8                                                       n-butyl acrylate    27.0                                                      i-butyl methacrylate                                                                              13.1                                                      t-butyl peroxy 2-ethylhexanoate                                                                   1.6                                                       total               101.6      parts                                          ______________________________________                                    

After 30 minutes from the completion of said addition, a mixed solutionof 0.5 part of t-butyl peroxy 2-ethylhexanoate and 5 parts of butylacetate was dropped in over 30 minutes and the mixture was maintained at120° C. for 1.5 hour.

The thus-obtained graft copolymer solution was a clear solution having anon-volatile content of 50.1%, a viscosity of Z₄ and a color number ofless than 1. When the resinous solution was applied on a glass and thesolvent was removed, a uniform clear coating was obtained.

EXAMPLE 3

400 parts of cellulose acetate butyrate (CAB-381-0.5) and 500 parts ofxylene were placed in a similar reaction vessel as stated in Example 1and gradually heated. After confirming the complete dissolution of CAB,80 parts of mono-butyl maleate, 0.8 part of dibutyl tinoxide and 20parts of xylene were added and the mixture was heated and stirred, whileintroducing nitrogen gas, at 145° to 150° C. for about 7 hours. Aftercompletion of the reaction, 720 parts of toluene, 200 parts of xyleneand 720 parts of butyl acetate were added to obtain a resinous solutionof cellulose acetate butyrate having a double bonding capable ofcopolymerizing with other monomers. By the GPC analysis, it was foundthat the h₁ /h₂ rate was 2.04, whereas the same rate of the starting CABresin was 0.12. The thus-obtained resinous solution was a clear solutionhaving a non-volatile content of 17.5%, a viscosity of H-I, and a colornumber of 1.

137.5 parts of the thus obtained resinous solution and 7.5 parts ofbutyl acetate were placed in a similar reaction vessel as used inExample 1, and the mixture was heated to 120° C. and stirred whileintroducing nitrogen gas. While keeping the same temperature, thefollowing mixture was added dropwise from a dropping funnel at aconstant speed in a period of 3 hours.

    ______________________________________                                        styrene             40.0       parts                                          2-hydroxyethyl methacrylate                                                                       16.2                                                      methyl methacrylate 30.9                                                      lauryl methacrylate 12.9                                                      t-butyl peroxy 2-ethylhexanoate                                                                   4.0                                                       total               104.0      parts                                          ______________________________________                                    

After 30 minutes from the completion of said addition, a mixed solutionof 0.5 part of t-butyl peroxy 2-ethylhexanoate and 5 parts of butylacetate was added dropwise over 30 minutes and thereafter, the mixturewas maintained at 120° C. for 1.5 hours. The thus-obtained graftcopolymer solution was a uniform clear solution having a non-volatilecontent of 50.0%, a viscosity of Z₃ and a color number of less than 1.When the resinous solution was applied on a glass plate and the solventwas removed, a uniform clear coating was obtained.

EXAMPLE 4

400 parts of cellulose acetate butyrate (CAB-381-0.5) and 500 parts ofxylene were placed in a similar reaction vessel as stated in Example 1and gradually heated. After confirming the complete dissolution of CAB,80 parts of dibutyl fumarate, 0.8 part of dibutyl tinoxide and 20 partsof xylene were added and the mixture was heated and stirred, whileintroducing nitrogen gas, at 145° to 150° C. for about 7 hours. Aftercompletion of the reaction, 720 parts of toluene, 200 parts of xyleneand 720 parts of butyl acetate were added to obtain a resinous solutionof cellulose acetate butyrate having a double bonding capable ofcopolymerizing with other monomers. By a GPC analysis, it was found thatthe h₁ /h₂ rate was 1.90, whereas the same rate of the starting CABresin was 0.13. The thus-obtained resinous solution was a clear solutionhaving a non-volatile content of 17.1%, a viscosity of J, and a colornumber of 1.

137.5 parts of thus obtained resinous solution and 7.5 parts of butylacetate were placed in a similar reaction vessel as used in Example 1,and the mixture was heated and stirred at 120° C. while introducingnitrogen gas. While keeping the same temperature, a following mixturewas dropped in from the dropping funnel at a constant speed in 3 hours.

    ______________________________________                                        styrene             20.0       parts                                          2-hydroxyethyl methacrylate                                                                       16.2                                                      methacrylic acid    1.1                                                       methyl methacrylate 9.5                                                       i-butyl methacrylate                                                                              50.4                                                      n-butyl acrylate    2.8                                                       t-butyl peroxy 2-ethylhexanoate                                                                   1.6                                                       total               101.6      parts                                          ______________________________________                                    

After 30 minutes from the completion of said addition, a mixed solutionof 0.5 part of t-butyl peroxy 2-ethylhexanoate and 5 parts of butylacetate was added dropwise over a period of 30 minutes and thereafter,the mixture was maintained at 120° C. for 1.5 hours. The thus-obtainedgraft copolymer solution was a uniform clear solution having anon-volatile content of 50.2%, a viscosity of Z₆ and a color number ofless than 1. When the resinous solution was applied on a glass plate andthe solvent was removed, a uniform clear coating was obtained.

COMPARATIVE EXAMPLE 1

50 parts of cellulose acetate butyrate (CAB-551-0.2), 62.5 parts ofxylene and 62.5 parts of toluene were placed in a similar reactionvessel as stated in Example 1 and gradually heated to 120° C. Afterconfirming the complete dissolution of CAB, the following mixture wasdropped in at the same temperature and at a constant speed, from adropping funnel in a period of 3 hours.

    ______________________________________                                        styrene             80.0       parts                                          2-hydroxyethyl methacrylate                                                                       32.4                                                      methacrylic acid    2.2                                                       methyl methacrylate 39.2                                                      n-butyl acrylate    24.0                                                      i-butyl methacrylate                                                                              22.2                                                      t-butyl peroxy 2-ethylhexanoate                                                                   8                                                         total               208.0      parts                                          ______________________________________                                    

After 30 minutes from the completion of said addition, a mixed solutionof 1.0 part of t-butyl peroxy 2-ethylhexanoate and 10 parts of butylacetate was added dropwise over a period of 30 minutes and thereafter,the mixture was maintained at 120° C. for 1.5 hours. The thus-obtainedgraft copolymer solution was a white turbid solution having anon-volatile content of 50.0%, and a viscosity of Z₄. When the resinoussolution was applied on a glass plate and the solvent was removed, awhite turbid coating was obtained.

COMPARATIVE EXAMPLE 2

400 parts of cellulose acetate butyrate (cAB-551-0.2) and 500 parts ofxylene were placed in a similar reaction vessel as stated in Example 1and gradually heated. After confirming the complete dissolution of CAB,80 parts of maleic anhydride, 0.8 part of dibutyl tinoxide and 20 partsof xylene were added and the mixture was heated and stirred, whileintroducing nitrogen gas, at 145° to 150° C. for about 10 hours. Aftercompletion of the reaction, 720 parts of toluene, 200 parts of xyleneand 720 parts of butyl acetate were added to obtain a resinous solutionof cellulose acetate butyrate.

By a GPC analysis, it was found that the h₁ /h₂ rate was 0.76, whereasthe same rate of the starting CAB resin was 0.13. The thus obtainedresinous solution was a clear solution having a non-volatile content of15.2%, a viscosity of A, and a color number of 1.

137.5 parts of the thus obtained resinous solution and 7.5 parts ofbutyl acetate were placed in a similar reaction vessel as used inExample 1, and the mixture was heated and stirred at 120° C. whileintroducing nitrogen gas. While keeping the same temperature, thefollowing mixture was added dropwise from a dropping funnel at aconstant speed in a period of 3 hours.

    ______________________________________                                        styrene             40.0       parts                                          2-hydroxyethyl methacrylate                                                                       16.2                                                      methacrylic acid    1.1                                                       methyl methacrylate 19.6                                                      n-butyl acrylate    12.0                                                      i-butyl methacrylate                                                                              11.1                                                      t-butyl peroxy 2-ethylhexanoate                                                                   4.0                                                       total               104.0      parts                                          ______________________________________                                    

After 30 minutes from the completion of said addition, a mixed solutionof 0.5 part of t-butyl peroxy 2-ethylhexanoate and 5 parts of butylacetate was added dropwise over a period of 30 minutes and thereafter,the mixture was maintained at 120° C. for 1.5 hour. The thus obtainedresinous solution was a white turbid solution having a non-volatilecontent of 50.0%, and a viscosity of Z₄. When the resinous solution wasapplied on a glass plate and the solvent was removed, a white turbidcoating was obtained.

The characteristics of the respective resins obtained in the abovesaidExamples and Comparative Examples and the film performances are shown inthe following Table 1.

                  TABLE 1                                                         ______________________________________                                                  Example           Comp. Example                                               1   2       3     4     1     2                                     ______________________________________                                        dried coating                                                                             ⊚                                                                    ⊚                                                                      ⊚                                                                  ⊚                                                                    ×                                                                             ×                             Solubility                                                                    toluene     ⊚                                                                    ⊚                                                                      ⊚                                                                  ⊚                                                                    ×                                                                             Δ                             xylene      ⊚                                                                    ⊚                                                                      ⊚                                                                  ⊚                                                                    ×                                                                             ×                             Compatibility                                                                 CAB-551-0.2 ⊚                                                                    ⊚                                                                      ⊚                                                                  ⊚                                                                    ×                                                                             ×                             1/4" nitrocellulose                                                                       ⊚                                                                    ⊚                                                                      ⊚                                                                  ⊚                                                                    □                                                                        □                        Acrydic A-801*                                                                            ⊚                                                                    ○                                                                              ⊚                                                                  ○                                                                            Δ                                                                             □                        Acrydic 44-127*                                                                           ⊚                                                                    ⊚                                                                      ○                                                                          ○                                                                            ×                                                                             Δ                             ______________________________________                                    

wherein:

dried coating:

A resinous solution was applied on a clear glass plate and dried at 110°C. for 1 hour. The resulting coating was evaluated by visual observationas follows:

    ______________________________________                                        ⊚                                                                           clear                                                            ○     slight clouding                                                  □ moderate clouding                                                Δ      white turbid                                                     ×      white turbid and phase separation                                ______________________________________                                    

Solubility:

1 g of resinous solution was taken in a test tube, mixed with 10 g oftoluene or xylene and the mixture was shaken well and then placed in astationary position at 20° C. for 24 hours. The resulting solution wasevaluated according to the following standards:

    ______________________________________                                        ⊚                                                                             clear                                                          ○       slight haze                                                    □   moderate haze                                                  Δ        haze and precipitation                                         ×        insoluble and complete                                                        phase separation                                               ______________________________________                                    

Compatibility:

Test resins were mixed together in a solid ratio of 1:1 and then appliedon a clear glass plate and dried at 110° C. for 1 hour. The film thusobtained was evaluated according to the same method as stated in thepreceding paragraph "dried coating".

Acrydic A-801: high styrene containing acrylic resin manufactured byDainihon Ink Co.

Acrydic 44-127: styrene free acrylic resin manufactured by Dainihon InkCo.

EXAMPLE 5 (preperation of CAB resinous solution)

Into a reaction vessel fitted with stirrer, a thermometer, a refluxcondenser and a nitrogen gas inlet, were placed 400 parts of celluloseacetate butyrate (CAB-551-0.2, trade mark, manufactured by EastmanChemical Products) and 475 parts of xylene and the mixture was heatedgradually. After confirming that the charged CAB was completelydissolved, 100 parts of mono-butyl maleic acid, 1.0 part of dibutyltinoxide and 25 parts of xylene were added and the mixture was heatedand stirred, while intorducing nitrogen gas, at 145° to 150° C. forabout 7 hours. After completion of the reaction, 1250 parts of tolueneand 250 parts of methyl isobutyl ketone were added to obtain a resinoussolution of CAB having a copolymerizable double bonding. The resinoussolution thus obtained was a clear solution having a non-volatilecontent of 19.0%, vicosity of A₂ to A₃ and color number of 1.

EXAMPLES 6-8 Preparation of CAB macromers

Using the same procedure as stated in Example 4 with the followingprescriptions shown in Table 2, various CAB resinous solutions wereprepared. The characteristics of these resins are shown in Table 2.

                  TABLE 2                                                         ______________________________________                                        Example No.     6         7       8                                           ______________________________________                                        CAB-551-0.01    400       --      --                                          CAB-531-1       --        400     --                                          CAB-381-0.1     --        --      400                                         monobutyl maleate                                                                             100       100     --                                          monoethyl maleate                                                                             --        --      95                                          dibutyl tinoxide                                                                              1.0       1.0     1.0                                         non-volatile content (%)                                                                      19.0      19.0    18.5                                        viscosity*      A.sub.4 -A.sub.5                                                                        Z.sub.1 -Z.sub.2                                                                      A.sub.2 -A.sub.3                            color number (Gardner)                                                                        1         1       1                                           ______________________________________                                         *Gardner bubble viscometer, 25° C.                                

EXAMPLE 9 (Preparation of CAB resinous solution)

Into a similar reaction vessel as used in Example 5, were placed 630parts of cellulose acetate butyrate (CAB-531-1) and 665 parts of xyleneand the mixture was gradually heated to dissolve said CAB. Thereafter,70 parts of monobutyl maleate, 0.7 part of dibutyl tinoxide and 35 partsof xylene were added and the mixture was heated and stirred, whileintroducing nitrogen gas, at 140° to 150° C. for about 7 hours. Aftercompletion of the reaction, the mixture was diluted with 1050 parts oftoluene and 350 parts of methyl isobutyl ketone to obtain a resinoussolution of cellulose acetate butyrate having a copolymerizable doublebonding. The thus obtained resinous solution was a clear solution havinga non-volatile content of 24%, a viscosity of Z₅ to Z₆ and a colornumber of 1.

EXAMPLE 10 (preparation of CAB graft acrylic resin solution)

Into a reaction vessel fitted with a thermometer, a stirrer, a refluxcondenser, a nitrogen gas inlet and a dropping funnel, were placed 100parts of CAB resinous solution obtained in Example 5, 10 parts oftoluene and 10 parts of methyl isobutyl ketone and the mixture washeated and stirred at 105° C. while introducing nitrogen gas. Whilemaintaining the same temperature, the following mixed solution of vinylmonomers and polymerization initiator was added dropwise at a constantspeed in a period of 3 hours.

    ______________________________________                                        styrene             10.0       parts                                          methyl methacrylate 35.3                                                      ethyl acrylate      38.4                                                      n-butyl acrylate    4.0                                                       2-hydroxyethyl methacrylate                                                                       11.6                                                      acrylic acid        0.7                                                       t-butyl peroxy 2-ethylhexanoate                                                                   2.0                                                       total               102.0      parts                                          ______________________________________                                    

After completion of said addition, a mixture of 0.5 part of t-butylperoxy 2-ethyl hexanoate and 20 parts of toluene was dropped in at aconstant speed in a time period of 60 minutes and thereafter, themixture was maintained at 105° C. for 1.5 hours. The thus obtained graftcopolymer solution was a uniform, clear solution having a non-volatilecontent of 50.2%, a viscosity of Z₂ to Z₃ and a color number of lessthan 1.

EXAMPLES 11 TO 19 Preparation of CAB graft acrylic resin solutions

Using the same procedures as stated in Example 10 with the materialsshown in Table 3, various CAB graft acrylic resin solutions 2 to 10 wereprepared, whose characteristics were shown in Table 3, together withthat of Example 10.

EXAMPLE 20 Preparation of CAB graft acrylic resin solution

Into a similar reaction vessel as used in Example 10, were placed 1089parts of CAB resinous solutions obtained in Example 14, 369 parts oftoluene and 4 parts of methyl isobutyl ketone and the mixture washeated, while stirring and introducing nitrogen gas, to 105° C. Then thefollowing mixed solution of vinyl monomers and polymerization initiatorwas dropped in at a constant speed from the dropping funnel, whilekeeping the temperature at 105° C., in 1.5 hour.

    ______________________________________                                        styrene             5.3        parts                                          methyl methacrylate 31.5                                                      ethyl methacrylate  7.4                                                       ethyl acrylate      46.4                                                      2-hydroxyethyl methacrylate                                                                       12.6                                                      t-butyl peroxy 2-ethylhexanoate                                                                   3.5                                                       toluene             70.0                                                      total               176.7      parts                                          ______________________________________                                    

After 30 minutes from the completion of said addition, a mixture of 0.5part of t-butyl peroxy 2-ethylhexanoate and 140 parts of toluene wasdropped in at a constant speed in 1 hour. Thereafter, the whole contentwas allowed to cool to obtain a resinous solution, whose characteristicsare shown in Table 3.

                                      TABLE 3                                     __________________________________________________________________________    Example No.    10  11  12   13  14  15 16 17  18 19  20                       __________________________________________________________________________    CAB resin. solution 1                                                                        100              100       50                                  CAB resin. solution 2                                                                            100              100       50                              CAB resin. solution 3  100             100       50                           CAB resin. solution 4       100                                               CAB resin. solution 5                                1089                     Vinyl monomers                                                                styrene        10.0                                                                              10.0                                                                              10.0     5.0 5.0                                                                              5.0                                                                              5.0    5.0 5.3                      methyl methacrylate                                                                          35.3                                                                              28.5                                                                              35.3 44.5                                                                              41.5                                                                              41.5                                                                             34.3                                                                             36.4                                                                              47.7                                                                             29.2                                                                              31.5                     ethyl methacrylate 6.7                 4.8                                                                              0.9    10.3                                                                              7.4                      ethyl acrylate 38.4                                                                              42.5                                                                              38.4 40.5                                                                              32.8                                                                              32.8                                                                             43.4                                                                             44.6                                                                              27.4                                                                             42.4                                                                              46.4                     n-butyl acrylate                                                                             4.0     4.0  2.7 8.3 8.3       12.0                            acrylic acid   0.7 0.7 0.7  0.7               1.3                             methacrylic acid                0.8 0.8                                                                              0.8                                                                              1.5    1.5                          2-hydroxyethyl methacrylate                                                                  11.6                                                                              11.6                                                                              11.6 11.6                                                                              11.6                                                                              11.6                                                                             11.6                                                                             11.6                                                                              11.6                                                                             11.6                                                                              12.6                     poly. initiator                                                               t-butyl peroxy-2-ethylhexanoate                                                              2.0     1.0  2.0 1.0 2.0                                                                              2.0                                                                              1.0    2.0 3.5                      azobisisobutylonitrile                                                                           0.9                        0.9                             Solvents                                                                      toluene        30  30  30   30  30  30 30 56.7                                                                              56.7                                                                             56.7                                                                              509                      methyl isobutyl ketone                                                                       10  10  10   10  10  10 10 13.3                                                                              13.3                                                                             13.3                                                                              4                        non-volatile content %                                                                       50.2                                                                              50.0                                                                              50.8 50.2                                                                              51.2                                                                              50.0                                                                             51.0                                                                             50.5                                                                              49.8                                                                             50.0                                                                              21.0                     viscosity      Z.sub.2 -Z.sub.3                                                                  Z-Z.sub.1                                                                         over Z.sub.6                                                                       Z-Z.sub.1                                                                         Z.sub.5 -Z.sub.6                                                                  U-V                                                                              Z.sub.6                                                                          Z.sub.1 -Z.sub.2                                                                  Y-Z                                                                              Z.sub.2 -Z.sub.3                                                                  Z.sub.3                  acid value (mg KOH/g solid)                                                                  13  13  13   13  13  13 13 13  13 13  5                        OH value (mg KOH/g solid)                                                                    50  50  50   50  50  50 50 50  50 50  53                       color number (Gardner)                                                                       1   1   1    1   1   1  1  1   1  1   1                        __________________________________________________________________________

COMPARATIVE EXAMPLE 3

Into a reaction vessel fitted with a stirrer, a thermometer, a refluxcondenser, a nitrogen gas inlet and a dropping funnel, were placed 30parts of toluene and 10 parts of methyl isobutyl ketone and the mixturewas heated and stirred at 105° C., while introducing nitrogen gas. Then,102 parts of the mixed solution of vinyl monomers and polymerizationinitiator shown in Example 10 were dropped in at a constant speed from adropping funnel, while keeping the temperature at 105° C., for 3 hours.

After 30 minutes from the completion of said addition, a mixture of 0.5part of t-butyl peroxy 2-ethylhexanoate and 20 parts of toluene wasadded dropwise at a constant speed in a period of 60 minutes. Aftercompletion of said addition, the mixture was maintained at 105° C. for aperiod of 1.5 hours. To this, a solution of 16 parts of CAB-551-0.2 in amixture of 20 parts of xylene, 26 parts of toluene and 10 parts ofmethyl isobutyl ketone was added while maintaining the temperature at105° C. and stirred for 30 minutes and allowed to cool. Thecharacteristics of the thus obtained varnish and resin are shown in thefollowing Table 4.

COMPARATIVE EXAMPLE 4

Into a similar reaction vessel as used in Comparative Example 3, wereplaced 16 parts of CAB-551-0.2, 20 parts of xylene, 56 parts of tolueneand 20 parts of methyl isobutyl ketone, and the mixture was, whileintroducing nitrogen gas, gradually heated to 105° C. At this stage, 102parts of the mixed solution of monomers and polymerization initiatorshown in Example 10 were dropped in from a dropping funnel at a constantspeed in a period of 3 hours.

After 30 minutes from the completion of said addition, a mixture of 0.5part of t-butyl peroxy 2-ethylhexanoate and 20 parts of toluene wasadded at a constant speed in a period of 60 minutes. After completion ofsaid addition, the mixture was maintained at 105° C. for 1.5 hours andthen allowed to cool. The characteristics of thus obtained varnish andresin are shown in Table 4.

COMPARATIVE EXAMPLE 5

Into a reactor, were placed 400 parts of cellulose acetate butyrate(CAB-551-0.2) and 475 parts of xylene and the mixture was graduallyheated to dissolve the CAB. After confirming the complete dissolution ofCAB, 100 parts of maleic anhydride, 1.0 part of dibutyl tinoxide and 25parts of xylene were added and the mixture was heated and stirred, whileintroducing nitrogen gas, at 145° to 150° C. for about 10 hours.Thereafter, the mixture was mixed with 1250 parts of toluene and 250parts of methyl isobutyl ketone to obtain a resinous solution, which wasclear and had a non-volatile content of 20%, a viscosity of C and acolor number of 1.

100 parts of thus obtained resinous solution were placed in, togetherwith 10 parts of toluene and 10 parts of methyl isobutyl ketone, asimilar reaction vessel as used in Comparative Example 3, and whileintroducing nitrogen gas, was heated and stirred. At the stage when thetemperature reached 105° C., there was added dropwise 102 parts of amixed solution of vinyl monomers and a polymerization initiator as shownin Example 10, at 105° C. over a period of 3 hours. After 30 minutesfrom the completion of said addition, a mixture of 0.5 part of t-butylperoxy 2-ethyl hexanoate and 20 parts of toluene was added dropwise at aconstant speed in a period of 60 minutes. Thereafter the mixture wasmaintained at 105° C. for 1.5 hours and allowed to cool. Thecharacteristics of thus obtained varnish and resin are shown in Table 4.

                  TABLE 4                                                         ______________________________________                                        Comparative Example No.                                                                         3         4       5                                         ______________________________________                                        non-volatile content %                                                                          50        50      50                                        viscosity         Z-Z.sub.1 Z.sub.1 -Z.sub.2                                                                      Z.sub.2                                   (Gardner, bubble viscometer                                                   25° C.)                                                                acid value        5         5       15                                        (mg KOH/g solid)                                                              OH value                                                                      (mg KOH/g solid)  50        50      50                                        color number (Gardner)                                                                          1         1        1                                        ______________________________________                                    

REFERENCE EXAMPLE 1 Preparation of acrylic resin for clear coat use

Into a reaction vessel fitted with a stirrer, a thermometer, a refluxcondenser, a nitrogen gas inlet and a dropping funnel, were placed 44parts of xylene, 10 parts of n-butanol and 20 parts of Solvesso 100(trade mark of aromatic petroleum solvent, manufactured by EssoStandard), and the mixture was heated and stirred, while introducingnitrogen gas. At the stage when the temperature reached 120° C., thefollowing mixed solution of vinyl monomers and polymerization initiatorwas dropped in from the dropping funnel at a constant speed, whilemaintaining the same temperature, in a period of 3 hours.

    ______________________________________                                        styrene             30        parts                                           n-butyl methacrylate                                                                              32.1                                                      lauryl methacrylate 18.6                                                      2-hydroxyethyl methacrylate                                                                       16.2      parts                                           methacrylic acid    3.1                                                       azobisisobutyronitrile                                                                            2                                                         total               102       parts                                           ______________________________________                                    

After 30 minutes from the completion of said addition, a mixture of 0.5part of t-butyl peroxy 2-ethylhexanoate and 5 parts of xylene was addeddropwise at a constant speed in a period of 30 minutes. Thereafter, themixture was maintained at 120° C. for 1.5 hours and then allowed tocool. The thus obtained acrylic resinous solution had a non-volatilecontent of 55.0%, a viscosity of W and a color number of less than 1.

REFERENCE EXAMPLE 2 Preparation of acrylic resinous solution for basecoat use

Into a reaction vessel fitted with a stirrer, a thermometer, a refluxcondenser, a nitrogen gas inlet and a dropping funnel, were placed 40parts of toluene and 10 parts of methyl isobutyl ketone and the mixturewas heated and stirred while introducing a nitrogen gas stream. At thestage when the temperature reached 105° C., the mixed solution of thefollowing vinyl monomers and polymerization initiator was added dropwiseat a constant speed while maintaining the same temperature in a periodof 3 hours.

    ______________________________________                                        styrene             10.0       parts                                          methyl methacrylate 21.4                                                      ethyl acrylate      40.6                                                      ethyl methacrylate  14.0                                                      2-hydroxyethyl methacrylate                                                                       12.0       parts                                          acrylic acid        2.0                                                       t-butyl peroxy 2-ethylhexanoate                                                                   1.0                                                       total               101.0      parts                                          ______________________________________                                    

After 30 minutes from the completion of said addition, a mixture of 0.4part of t-butyl peroxy 2-ethylhexanoate and 15 parts of toluene wasadded dropwise at a constant speed in a period of 60 minutes andthereafter maintained at 105° C. for 1.5 hours. The mixture was thendiluted with 35 parts of toluene and allowed to cool. The thus-obtainedacrylic resin solution had a non-volatile content of 50.0%, a viscosityof Y-Z and a color number of less than 1.

EXAMPLE 21

CAB graft acrylic resin and other components shown in the followingTable 5 were taken in a tin and mixed well with disper for 15 minutes,thereby obtaining the respective metallic base paints A to K.

                                      TABLE 5                                     __________________________________________________________________________    Paint       A  B  C  D  E  F  G  H  I  J  K                                   __________________________________________________________________________    Ex. No. for the CAB                                                                       10 11 12 13 14 15 16 17 18 19 20                                  graft acrylic resin used                                                      CAB graft acrylic                                                                         160                                                                              160                                                                              160                                                                              160                                                                              160                                                                              160                                                                              160                                                                              160                                                                              160                                                                              160                                                                              55                                  resin solution                                                                U-van 20SE60.sup.1                                                                        33 33 33 33 33 33 33 33 33 33 33                                  Alpaste 1109 MA.sup.2                                                                     15 15 15 15 15 15 15 15 15 15 15                                  toluene     10 10 10 10 10 10 10 10 10 10 10                                  ethyl acetate                                                                             5  5  5  5  5  5  5  5  5  5  5                                   n-butanol   5  5  5  5  5  5  5  5  5  5  5                                   Modaflow.sup.3                                                                            0.2                                                                              0.2                                                                              0.2                                                                              0.2                                                                              0.2                                                                              0.2                                                                              0.2                                                                              0.2                                                                              0.2                                                                              0.2                                                                              0.2                                 acrylic resin                             138                                 solution.sup.4                                                                __________________________________________________________________________     .sup.1 melamine resin manufactured by Mitsuitohatsu                           .sup.2 aluminum pigment manufactured by Toyo Aluminum                         .sup.3 levering agent manufactured by Monsanto                                .sup.4 Acrylic resin solution for base coat use, prepared by the method o     Ref. Example 2                                                                Next, a clear paint was prepared by using the materials shown below and       mixing them by disper for 15 minutes.                                        acrylic resin solution.sup.5                                                             140                                                                              parts                                                           U-van 20 SE 60                                                                           50                                                                 Solvesso 150.sup.6                                                                       20                                                                 n-butanol  5                                                                  UV absorber                                                                              1                                                                  Modaflow   0.2                                                                 .sup.5 acrylic resin solution for clear coat use prepared by Ref. Example     1                                                                             .sup.6 aromatic solvent, manufactured by Esso Standard                   

A series of test pieces were prepared by using zinc phosphated dullsteel plates (each 0.8×300×300 mm) and subjecting them in sequentialorder, to a cationic electrodeposition, an inter coat application andsanding. Onto the test pieces thus obtained, the respective metallicbase paint previously added with a mixed solvent of toluene:ethylacetate:Solvesso 150 (5:3:2) to adjust the viscosity to 14 seconds a #4Ford Cup was applied to give a wet thickness of 20 microns by 2 stagesand 1 minute interval application method. For this coating, was used anautomatic applicator fitted with wider 61. The atomizing pressure was 4Kg/cm² and the booth atmosphere was maintained at a temperature of 25±2°C. and a humidity of 75 ±5%. After 3 minutes setting in the boothatmosphere, a clear paint previously adjusted to a viscosity of 27seconds by a #4 Ford Cup with a mixed solvent of Solvesso 100:Solvesso150 (2:1) was applied so as to give a wet thickness of 35 microns. Thiswas then allowed to set for 5 minutes and baked at 140° C. for 20minutes. The film properties of the thus obtained coating are shown inthe following Table 6.

                                      TABLE 6                                     __________________________________________________________________________    metallic paint                                                                           A  B  C  D  E  F  G  H  I  J  K                                    __________________________________________________________________________    Appearance                                                                    60° gloss*                                                                        96 97 96 97 97 97 96 94 94 94 97                                   metallic feeling*                                                                        ⊚                                                                 ⊚                                                                 ⊚                                                                 ⊚                                                                 ⊚                                                                 ⊚                                                                 ⊚                                                                 ⊚                                                                 ⊚                                                                 ⊚                                                                 ⊚                     L value*   67.5                                                                             67.7                                                                             67.6                                                                             67.8                                                                             67.9                                                                             67.6                                                                             67.3                                                                             66.4                                                                             66.5                                                                             66.5                                                                             67.8                                 metallic mark*                                                                           ⊚                                                                 ⊚                                                                 ⊚                                                                 ⊚                                                                 ⊚                                                                 ⊚                                                                 ⊚                                                                 ⊚                                                                 ⊚                                                                 ⊚                                                                 ⊚                     visual appearance*                                                                       ⊚                                                                 ⊚                                                                 ⊚                                                                 ⊚                                                                 ⊚                                                                 ⊚                                                                 ⊚                                                                 ⊚                                                                 ⊚                                                                 ⊚⊚        240 hrs. humidity test                                                        blister    10 10 10 10 10 10 10 10 10 10 10                                   __________________________________________________________________________     wherein *marks represent the following:                                  

    60° gloss.                                                                     60° mirror reflectance by JIS-K-5400                           metalic feeling.                                                                      visual observation                                                    L value whiteness by Hanter's color indication the bigger the number, the             whiter the                                                                    color and the more the metallic feeling                               metallic mark                                                                         aluminum arrangement on the whole surface was checked by naked                eyes                                                                  blister gloss and smoothness were judged by visual observation by 10                  point system                                                           Metallic feeling, metal irregularity and visual appearance were judged        according to the following standards                                          ⊚ quite excellent                                               ○  excellent                                                          Δ somewhat no good                                                      × no good                                                          

COMPARATIVE EXAMPLE 6

Metallic base paints L, M and N were prepared as in Example 21 exceptingCAB graft acrylic resin solutions obtained in Comparative Examples 3 to5 was used. The similar tests as given in Example 21 were repeated withthese base paints and the following results were obtained.

                  TABLE 7                                                         ______________________________________                                        metallic paint                                                                              L        M         N                                            ______________________________________                                        60° gloss                                                                            92       93        92                                           metallic feeling                                                                            Δ  Δ   Δ                                      L value       62.2     62.3      61.6                                         metallic mark Δ  Δ   Δ                                      visual appearance                                                                           ○ ○  ○                                     blister       10       10        10                                           ______________________________________                                    

What is claimed is:
 1. A coating composition to be used as a base coatin a 2-coat and 1-bake coating system comprising as a resinous vehiclean acrylic graft copolymer and a crosslinking agent, said acrylic graftcopolymer being obtained by reacting a cellulose ester with a mono- ordi-ester of an acid selected from the group consisting of a mono-esterof maleic acid, a mono-ester of fumaric acid, a di-ester of maleic acidand a di-ester of fumaric acid so as to chemically combine the celluloseester and the mono- or di-ester of said acid through an ester bondingand copolymerizing the thus obtained cellulose acetate butyrate bearinga copolymerizable double bonding with other polymerizable monomer(s). 2.The coating composition according to claim 1 wherein the crosslinkingagent is an amino resin.
 3. The coating composition according to claim 1further containing an other resin for coating use, a solvent, a coloringagent, a filler, a surface conditioner, and a metallic powder.